Various types of industrial liquid dispensing applications have requirements related to dispensing small, discrete amounts of liquid while achieving high degrees of accuracy, uniformity and/or repeatability during successive and often rapid dispense cycles. Positive displacement pumps are used to achieve at least some of these purposes. However, various applications require dispense amounts, cycle times and other process parameters that typical positive displacement pumps cannot meet. On the other hand, apparatus that can meet these other process parameters may not dispense with the required accuracy, repeatability and/or uniformity. For example, dispensers may utilize elements that are acted upon by air pressure or mechanical devices, such as stepper drives, at a location remote from the point of application. Under these circumstances, the deposition amount or volume of discharged liquid can vary depending on a number of factors. This may require that the user continually adjust system settings in order to maintain uniform application rates. Even so, the desired or required degree of accuracy and uniformity may not be achieved. In addition, the size of a desired liquid deposition is often very small, such as on the order of 10−7 in.3 or less, and this can create process control issues. Also, many of the materials that are used in industry are curable or hardenable materials, such as epoxies, which can create additional challenges related to maintenance.
Various forms of jetting dispensers are known and have been used successfully to dispense small amounts of viscous liquids with a high degree of accuracy, uniformity and repeatability. Challenges that remain with regard to jetting technology include the challenge of maintaining the inner components and passages clear of residual liquid material between dispense operations so that repeated use of the jetting dispenser can occur without any negative effects of cured or hardened material within the device. In addition, there are times when liquid satellite formation is a problem. This involves the formation of additional small amounts of the liquid around the dispensed amount. Satellite formations and/or undesired atomization may negatively affect the deposition pattern that is desired on the intended substrate. Finally, leakage of liquid from the outlet of a jetting dispenser between dispense cycles can be a problem.
It would therefore be desirable to provide a liquid dispenser that addresses concerns such as those mentioned above, and can lessen the need to clean various components and passages, lessen satellite formation and atomization, and prevent leakage of liquid from the dispensing outlet between dispense cycles.